A BIOS has been widely used as firmware for interface between an operating system and hardware, but EFI (Extensible Firmware Interface) has been gradually employed instead of the BIOS.
In a system employing EFI, a conventional MBR (Master Boot Record) is not employed at booting of an operating system. The operating system is booted by an EFI boot manager. The EFI boot manager is executed by a CPU based on a boot file in an EFI system partition of an HDD.
The EFI system partition is basically located at a leading part of the HDD and is formatted by a FAT32 file system. The boot file is stored in, for example, EFI\<vender name> folder. A booting sequence of the boot file can be changed based on a boot variable indicating a path of a file stored in a nonvolatile memory of the EFI system. If there is no setting, a file in a default file path (EFI\Boot\Bootx64.EFI for x64) is booted.
If the booting sequence of the boot file is changed, the booting sequence can be changed based on a boot variable. However, the booting sequence is not often referred to for equipment of the EFI.